The CAN bus system has become widespread for communication between two or more bus users such as sensor(s), control unit(s), etc. In the CAN bus system, messages are transmitted with the aid of the CAN protocol, as described in the CAN specification in ISO 11898. As the number of intelligent sensors grows and control units become increasingly networked in vehicles, the number of user stations on the CAN bus and the data volume on the CAN bus are continually increasing.
Patent document DE 10 000 305 A1 discusses the controller area network (CAN) and an enhancement of the CAN, referred to as time-triggered CAN (TTCAN). The method for controlling media access used in the CAN is based on bit-wise arbitration. In the CAN, the bit-wise arbitration is carried out based on a leading identifier within the message that is to be transmitted via the bus.
As already discussed in DE 10 2012 200 997, during bit-wise arbitration multiple user stations may simultaneously transmit data to the bus system without interfering with the data transmission.
Technologies such as CAN FD have recently been provided in which messages are transmitted, etc., corresponding to the specification “CAN with Flexible Data-Rate, Specification Version 1.0” (source: http://www.semiconductors.bosch.de). In such technologies, the maximum possible data rate is increased beyond a value of 1 Mbit/s by using higher clocking in the area of the data fields.
The bus topology plays a major role for the signal integrity, and thus for rapid data transmission. In particular, it is problematic that reflections arise during the data transmission at each branch of the data lines for a user station of a CAN bus system. These reflections are superimposed on the transmitted signals and interfere with reception by the receiver. The larger the reflections, the slower the data rate that must be selected in order to still be able to reliably transmit the signal.
The most important demands on a CAN high-speed transceiver (CAN HS transceiver), apart from adhering to the functional parameters, are to meet the requirements with regard to:
emissions,
direct power injection (DPI), which is a method for measuring the immunity to interference in the range of electromagnetic compatibility (EMC), and
electrostatic discharge (ESD).
With the introduction of CAN FD by some CAN users, bit rates of higher than 1 Mbit per second (1 Mbps), 2 Mbps, 4 Mbps, and possibly higher are now being used. It is problematic that, despite increasing the data rate for the CAN bus system, the manufacturers call for the same values for the emission limits as for the data rate for a conventional CAN bus system, which is configured according to “Hardware Requirements for CAN Interfaces 1.3,” for example. At the present time, CAN FD cannot comply with these limits when the higher bit rates are used. The reason for noncompliance with the limits is the increased energy density for the same transceiver, since more edges per unit time are driven in the CAN signal.
Another requirement which cannot be met by the related art is the demand by the CAN users for the emission limits to be met at the two bus lines, which are ±10 ohms, even for asymmetrical resistances in the decoupling network. This demand should reflect the different line resistances of the two bus lines in the actual vehicle.